This invention relates to a plastic processing system, and more particularly to a drive system for moving open-topped receptacles such as crowns along a conveyance path and accurately positioning extrudate segments into the centers thereof.
In high speed crown making systems, a pellet of extruded thermoplastic material is deposited into each crown shell by controlling the rate of extrusion of the thermoplastic material and then directing this material through one or more rotating cutting blades timed to the feed rate of the crowns past the depositing station. To ensure that the severed segments of thermoplastic material are consistently deposited in the centers of the traveling crowns, the speed of the conveyor, the feed rate of the thermoplastic material, and the angular velocity of the cutting blades are maintained in a proportional relationship that varies with the rate of production. For any rate of production, the feed rate of the crowns must be compatible with the cutting rate of the blades, and these in turn must be compatible with the minimum cooling rate of the formed liner.
The characteristics of the various types of thermoplastic material available introduce other considerations into the placement of the extruded segments. When PVC compositions are utilized, the crown shells are heated before the segments of lining material are deposited centrally therein. When PVC-free materials are utilized, the crown shells are not heated until after the segments have been deposited. Because PVC-free segments tend to slide, it is necessary to compensate by depositing them so that they are slightly offset from the shell centers. Thus, for a crown processing apparatus to be adapted for use with both PVC and PVC-free lining materials, it is necessary to provide some means for adjusting the location of the shells on which the segments are deposited.
An illustrative apparatus for forming liners in crowns is described in U.S. Pat. No. 3,360,827 to Aichele, wherein a rotatably mounted blade is rotated in synchronism with the movement of a conveyor. The cutting blade is rotated at a uniform speed that is directly proportional to the speed of shell conveyance. During each rotation of the knife, a segment or pellet of extruded thermoplastic polymer is severed, and the radial tip of a blade enters and exits the recess of a shell as it is conveyed, thereby depositing the polymer pellet centrally therein. A subsequent operation forms the pellet into a desired liner shape.
Although the high feed rate apparatus disclosed in the Aichele patent operates satisfactorily for providing thermoplastic material in bottle caps or crowns, difficulties have been encountered in insuring that the thermoplastic material is deposited in the center of the receiving crown. Even relatively minor variations in timing can have a substantial effect on the accuracy of the Aichele device. It will be appreciated that with certain lining materials, if the severed segment is deposited at any place other than the center of the receiving crown, a liner of non-uniform thickness and/or misaligned position will result. Thus, when timing variations occur, it is necessary to stop operating the Aichele device until timing adjustments can be made, thereby causing considerable losses in time and production. Another drawback of the Aichele system is that there are no provisions for adjusting the tension in the drive belt during production.
In U.S. Pat. No. 3,825,044 to Lidikay, there is disclosed a crown lining apparatus which includes a pair of counter rotating cutting blades and a mechanism for making timing adjustments to the blades without stopping the apparatus. In addition to a drive sprocket for driving the belt and a pair of driven sprockets for rotating the cutting blades, The Lidikay device provides an elongated carrier member which carries a pair of spaced idler sprocket wheels and a shiftable idler pulley. The carrier defines a plurality of teeth and is shifted laterally by rotating a spur gear having teeth which engage the teeth on the carrier member. By laterally shifting the carrier, the belt can be momentarily advanced or withdrawn relative to the driven sprockets, thereby changing the timing of the cutting blades. Like the Aichele device, however, the Lidikay system also lacks any provision for selectively adjusting the tension of the belt during operation.